1. Field of the Invention
The present invention relates to a mold for making a double layer molded product composed of a skin layer and an inner layer.
2. Description of the Related Art
Molded products of sandwich construction are typically double layer molded products composed of a skin and a core which are formed from different synthetic resins. Hollow molded products are also double layer molded products in that they are composed of a skin of synthetic resin with a hollow portion (e.g. gas) formed therewithin.
When making a double layer molded product, such as one of sandwich construction or one which is hollow molded, a skin-forming material is first injected into a cavity, and then an inner-forming material (a core-forming resin or fluid for forming a hollow portion) is injected into the skin-forming material.
As shown in FIGS. 9 and 10, conventional molds for making double layer molded products have a cavity 91. An end portion of the cavity 91 communicates with a film gate 92. The film gate 92 is connected to a synthetic resin or other material injector via a runner 93 and a sprue 94.
When making a molded product of sandwich construction, a softened skin-forming material 81 is injected into the cavity 91 through the film gate 92. Then a softened core-forming synthetic resin 82 is injected into the softened synthetic resin 81 through the film gate 92.
When making a hollow molded product, the inner, hollow part may be formed by injecting a fluid, such as a gas, in lieu of the softened core-forming material 82.
However, typically the inner, core-forming material is not properly injected in the vicinity of the gate of the conventional mold. More particularly, with reference to FIGS. 9 and 10, the flow of the injected inner-forming material is greatly influenced by the softness of the skin and the pressure gradient. A relatively great pressure gradient is exerted in the direction in which the material is injected, whereas a lesser pressure gradient is exerted transverse thereto. Thus, the longitudinal direction of the cavity 91 receives a relatively sharp pressure gradient. On the other hand, the direction across the cavity 91 receives a lesser pressure gradient.
Thus, the core-forming material 82, as an inner-forming material, is injected so as to be long and narrow along the longitudinal direction of the cavity 91. As a result, the thickness of the core increases from the gate to the more remote portions of the mold, resulting in an unevenness in core thickness.